1. Field of the Invention
This invention relates to a process for direct transfer printing of designs on fabrics using electrostatic printing techniques. More specifically, it relates to an improved process for electrostatic direct transfer printing of a design on a fabric wherein the fabric has a surface inherent resistivity, as measured at a temperature of 20.degree. C. and a relative humidity of 65% of the fabric to about 1.times. 10.sup.6 to about 1.times. 10.sup.14 ohms. The invention also relates to an improved process for electrostatic direct transfer printing of a design on a fabric wherein the transfer is performed by corona discharge while a sheet having a volume inherent resistivity of 1.times. 10.sup.6 to 1.times. 10.sup.20 ohms is superimposed on that surface of the fabric which is opposite the surface to be imprinted.
2. Description of the Prior Art
Transfer printing methods using an electrostatic photographic technique, usually called electrostatic printing, include, for example, a xerographic method and an electrofax method. For example, the xerographic method comprises forming a positive electrostatic latent image on an amorphous selenium photosensitive layer, developing the latent image with a negatively charged colored powder (to be referred to hereinafter as a "toner") composed of a colorant such as a dye or pigment and a resin capable of being charged, superimposing a paper sheet on the developed image, and applying a corona discharge to the paper sheet thereby to transfer the toner image on the photosensitive layer to the paper sheet. The electrofax method involves using zinc oxide as a photosensitive layer, developing a latent image formed on it with a positively charged toner, and then transferring the developed toner image to a paper sheet using a negative corona discharge.
When paper sheets are used as a material to be imprinted in the above-described methods, corona discharge transfer of the developed images on the photosensitive layer to paper can be performed satisfactorily to obtain electrostatically transferred printed images having a high density and sharpness, and in fact, these methods have been widely used commercially. However, where fabrics are used as a material to be imprinted, electrostatic transfer printing provides extremely poor results. Therefore, methods using fabrics have scarcely been practiced commercially, or have had to include complicated steps. The serious difficulty in this case lies in the transfer of the developed toner image to the fabric. Because the efficiency of transfer in this case is very poor, feasible image densities and sharpness cannot be obtained. The contamination of the back of the printed fabrics is also high, and degrades the commercial value of the printed goods. With a view to avoiding these difficulties, it has been the previous practice to transfer the developed toner image first to a paper sheet, and then transfer it to a fabric by heating under pressure. Or when a sublimable dye is used as the colorant, a transfer sheet having a developed toner image thereon is superimposed on a fabric and heated under pressure to sublime and transfer only the dye to the fabric. These complicated steps naturally add to the cost of production as a result of the loss of the dye, etc. Furthermore, since one additional step is required for transfer, the image ultimately transferred tends to be vague and poor in quality. Further, contamination of the back surface of the fabrics with the toner which passes through the openings in the structure of the fabrics (hereinafter back side contamination) occurs with this technique. These difficulties preclude the use of the electrostatic printing process in printing of designs on fabrics.